1. Field of the Invention
The present invention relates to magnetooptic garnets adaptable for use in Faraday rotators which are used in optical fiber transmission systems.
2. Description of the Prior Art
As disclosed in U.S. Pat. No. 4,522,473 granted to Hibiya et al, Faraday rotators are used as optical isolators, optical circulators, and optical switches in optical fiber transmission systems.
The Faraday rotator comprises a non-magnetic garnet substrate and a magnetooptic garnet film. The magnetooptic garnet is epitaxially grown on the substrate.
Recently, it has been proposed to use an epitaxially grown (GdBi).sub.3 (FeAlGa).sub.5 O.sub.12 garnet as the magnetooptic garnet film of the Faraday rotator in order to reduce a cost of the Faraday rotator. A reference is made to a paper WK1 in Conference on Optical Fiber Communication held in San Diego, Calif., U.S.A. in February, 1985.
Faraday rotation coefficient of (GdBi).sub.3 (FeAlGa).sub.5 O.sub.12 garnet has a large temperature characteristic and considerably varies in dependence on a circumference temperature. Even if an angle of Faraday rotation of a Faraday rotator is insured to be 45.degree. angle at the room temperature which is necessary for use in an isolator, the Faraday rotation angle changes by the circumference temperature variation so that isolation is degraded.